In contrast with volatile data bits, non-volatile data bits maintain stored digital data for relatively extended periods of time without need to maintain power to the data bit. Such non-volatile data bits include read-only data bits, made from various semiconductor devices and known in the art as ROM, and flash data bits, traditionally made from floating-gate transistors. Such non-volatile data bits are electrically addressed and thus are faster to access than, for instance, mechanically addressed data storage systems such as magnetic storage (for instance, hard disks) and optical storage (for instance, CD-ROMs). However, non-volatile data bits have historically contrasted unfavorably with volatile memory and mechanically addressed data storage in terms of cost, efficiency and utility. While both volatile and mechanically addressed storage is relatively cheap to produce, densely packed and freely writeable and rewriteable, non-volatile memory has historically been expensive, large and with limitations on how many times the cell may be written to, as with a flash data bit, or not subject to being rewritten at all, as with ROM cells.
Recent developments in the technology and production of flash cells, however, have begun to make flash memory relatively cost effective for various common applications. In applications accustomed to the use of relatively high-power consumption volatile memory, the use of flash memory in and of itself may produce considerable power savings over volatile memory. However, particularly in applications which rely on low power consumption, the use of flash cells may nevertheless produce undesirably high power consumption.
In part, the power consumption of flash memory systems derives not only from the individual flash data bits themselves which comprise the array but also from the infrastructure built around the individual cells which permit the reading and writing of data to the cells. In particular, and as is well known in the art, the operation by which the contents of a flash data bit are read involves biasing the cell with a voltage and sensing the impact of the cell current. On the basis of an amount of cell current, the data state of the cell may be determined. Current sensing carries the advantages of being relatively unsusceptible to variances in the characteristics of individual flash cells and resilience against noise interference.